A fuel supply pump compresses fuel fed from a fuel tank, and pressurizes the fuel, so that the pressurized fuel is supplied to a fuel injecting apparatus. In a conventional fuel supply pump disclosed in JP-A-2002-310039 shown in FIG. 9, a fuel supply pump 50 has a camshaft 54, a cam ring 55 and a plunger 56. The camshaft 54 is rotatably arranged in a housing 51. The camshaft 54 has a cam portion 542. The cam ring 55 is rotatably arranged on the outer periphery of the cam portion 542 such that the cam ring 55 is rotatable with respect to the cam portion 542, so that the cam ring 55 vertically reciprocates. The plunger 56 connects with the cam ring 55 such that the plunger 56 vertically reciprocates in conjunction with the cam ring 55. The end portion of the plunger 56, which is opposite to the connecting portion between the plunger 56 and the cam ring 55, is inserted into a pressure chamber 52, into which high-pressure fuel is introduced. When the plunger 56 reaches the top dead center of the plunger 56, fuel introduced into the pressure chamber 52 is pressurized, and the pressurized fuel is supplied to the fuel injecting apparatus.
The outer circumferential periphery of the cam portion 542 defines an oil groove 543. Low-pressure oil, which flows into a cam chamber 53, is introduced into the oil groove 543 as lubricating oil. The lubricating oil is entirely distributed from the oil groove 543 to the outer circumferential periphery of the cam portion 542. Thus, seizure between the cam portion 542 and the cam ring 55 is restricted.
In the conventional fuel supply pump 50, washer members 60 are respectively provided between the axial end faces of the cam ring 55 and flat faces of the housing 51 that oppose to the axial end faces of the cam portion 542. Each washer member 60 aligns the camshaft 54 in the axial direction. In this structure, clearance, which is formed between each axial end face of the cam ring 55 and the opposing axial end face of the corresponding washer member 60, is formed to be small. When the clearance is small, an amount of lubricating oil introduced from the cam chamber 53 into the clearance becomes small, and the lubricating oil may not be entirely distributed over the outer circumferential periphery of the cam portion 542. In this case, seizure may occur and the fuel supply pump 50 may be damaged.